Straw-sheaf-like Co3O4 for preparation of an electrochemical non-enzymatic glucose sensor.

3D straw-sheaf-like cobalt oxide (SS-Co3O4) was prepared via the hydrothermal method and inert gas calcination of precursors without the assistance of any template or surfactant. It was composed of numerous nanoneedles with a length of ~ 8 µm and a diameter of ~ 30 nm strongly tied in the center. The SS-Co3O4 exhibited high crystallinity, a large surface area (39.01 m2.g-1), a smaller pore size (6 nm), and lower charge transfer resistance (Rct = 9.35 Ω) at the electrode/electrolyte interface. A non-enzymatic glucose oxidizing electrode fabricated with SS-Co3O4 showed a high sensitivity (669 µA.mM-1.cm-2), wide linear range (0.04-4.85 mM), low limit of detection (0.31 µM), good selectivity, fast response time (5 s), and high reproducibility with a relative standard deviation of 2.25%. In addition, its robust structure demonstrated excellent electrochemical stability by retaining 83.8% of the initial sensitivity when its current density vs. time response was measured for 75 min in bare electrolytes prior to the glucose-sensing test. Furthermore, it demonstrated excellent repeatability performance by retaining 87.0% of the initial sensitivity when a single electrode was tested for 4 cycles. The proposed robust structured 3D SS-Co3O4 electrode successfully responds to the content of glucose in human saliva, which substantially proves its suitability in practical application. The synthesis technique is advantageous to prepare other metal oxides with interesting morphology and robust structure for the development of more reliable non-enzymatic glucometers and other electrochemical devices.

Enhanced Electrocatalytic Oxidation of Small Organic Molecules on Platinum-Gold Nanowires: Influence of the Surface Structure and Pt-Pt/Pt-Au Pair Site Density.

The electrochemical oxidation of small organic molecules (SOMs) such as methanol and glucose is a critical process and has relevant applications in fuel cells and sensors. A key challenge in SOM oxidation is the poisoning of the surface by carbon monoxide (CO) and other partially oxidized intermediates, which is attributed to the presence of Pt-Pt pair sites. A promising pathway for overcoming this challenge is to develop catalysts that selectively oxidize SOMs via "direct" pathways that do not form CO as a primary intermediate. In this report, we utilize an ambient, template-based approach to prepare PtAu alloy nanowires with tunable compositions. X-ray photoelectron spectroscopy measurements reveal that the surface composition matches that of the bulk composition after synthesis. Monte Carlo method simulations of the surface structure of PtAu alloys with varying coverage of oxygen adsorbates and varying degrees of oxygen adsorption strength reveal that oxygen adsorption under electrochemical conditions enriches the surface with Pt and a large fraction of Pt-Pt sites remain on the surface even with the Au content of up to 50%. Electrochemical properties and the catalytic performance measurements of the PtAu nanowires for the oxidation of methanol and glucose reveal that the mechanistic pathways that produce CO are suppressed by the addition of relatively small quantities of Au (∼10%), and CO formation can be completely suppressed by 50% Au. The suppression of CO formation with small quantities of Au suggests that the presence of Pt-Au pair sites may be more important in determining the mechanism of SOM oxidation rather than Pt-Pt pair site density.

A facile and sensitive electrochemical sensor for non-enzymatic glucose detection based on three-dimensional flexible polyurethane sponge decorated with nickel hydroxide.

A novel three-dimensional nickel hydroxide/polyurethane (Ni(OH)2/PU) electrode was prepared by a simple and environmentally friendly method and used for non-enzymatic detection of glucose. The Ni(OH)2/PU electrode was obtained by one-pot hydrothermal method of loading nickel hydroxide on a cheap, easily available and flexible polyurethane sponge, which is facile and energy-saving. The porous structure of the polyurethane sponge provides a large surface area and a rich electrochemical active site for the electrode, which is beneficial to the oxidation reaction of glucose on the surface of the electrode with Ni(OH)2. The Ni(OH)2/PU electrode structure was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry test was used to study the catalytic performance of Ni(OH)2/PU electrode for oxidation of glucose and the chronoamperometry was used to investigate the detection performance of Ni(OH)2/PU electrode on glucose. The results indicate that this non-enzymatic glucose sensor had a high sensitivity of 2845 µA mM-1 cm-2, a low detection limit of 0.32 µM (S/N = 3), a detection range of 0.01-2.06 mM and response time of less than 5 s. In addition, the Ni(OH)2/PU electrode had excellent selectivity, reproducibility and stability and also exhibited effective detection of glucose in fetal bovine serum (FBS). In summary, Ni(OH)2/PU electrode had broad prospects as an excellent candidate for non-enzymatic glucose sensors. The study also opens up a facile and energy-saving approach for preparing three-dimensional (3D) functionalized polymer electrode via hydrothermal method as electrochemical sensors.

Dual functional rhodium oxide nanocorals enabled sensor for both non-enzymatic glucose and solid-state pH sensing.

Both pH-sensitive and glucose-responsive rhodium oxide nanocorals (Rh2O3 NCs) were synthesized through electrospinning followed by high-temperature calcination. The as-prepared Rh2O3 NCs were systematically characterized using various advanced techniques including scanning electron microscopy, X-ray powder diffraction and Raman spectroscopy, and then employed as a dual functional nanomaterial to fabricate a dual sensor for both non-enzymatic glucose sensing and solid-state pH monitoring. The sensing performance of the Rh2O3 NCs based dual sensor toward pH and glucose was evaluated using open circuit potential, cyclic voltammetry and amperometric techniques, respectively. The results show that the as-prepared Rh2O3 NCs not only maintain accurate and reversible pH sensitivity of Rh2O3, but also demonstrate a good electrocatalytic activity toward glucose oxidation in alkaline medium with a sensitivity of 11.46 µA mM-1 cm-2, a limit of detection of 3.1 µM (S/N = 3), and a reasonable selectivity against various interferents in non-enzymatic glucose detection. Its accuracy in determining glucose in human serum samples was further demonstrated. These features indicate that the as-prepared Rh2O3 NCs hold great promise as a dual-functional sensing material in the development of a high-performance sensor forManjakkal both solid-state pH and non-enzymatic glucose sensing.

Designing and facilely synthesizing a series of cobalt nitride (Co4N) nanocatalysts as non-enzymatic glucose sensors: A comparative study toward the influences of material structures on electrocatalytic activities.

Designing high-efficiency electrocatalysts for glucose concentration detection plays a pivotal role in developing various non-enzymatic glucose detection devices. Herein, we have successfully designed and synthesized various cobalt nitrides (Co4N) by using different weak bases (i.e. hexamethylenetetramine (HMT), urea, and ammonium hydroxide (AH)) through nitridation treatment in ammonia (NH3) atmosphere. Physical characterization results demonstrate that Co4N-NSs (nanosheets) with vast meso/macropores and large BET surface are successfully constructed once adding carbon paper and HMT into precursors. As the synergistic effect of metallic character of Co4N phase, excellent electroconductibility of pyrolytic carbon, and large surface area, Co4N-NSs surfaces can form more Co4+ active sites in electrochemical reaction processes. Meanwhile, the abundant meso/macroporous structures constructed in Co4N-NSs further promoted its mass transfer ability. Benefitting from the above mentioned advantages, Co4N-NSs therefore exhibit more excellent glucose oxidation ability than another three control samples (i.e. Co4N-HMT, Co4N-Urea and Co4N-AH). When used for glucose detection, the optimal Co4N-NSs display excellent detection parameters as well, such as: a wide linear range of 0.6-10.0mM, a large sensitivity of 1137.2uAcm-2mM-1 glucose, a low detection limit of 0.1µM, a small response time of 1.7s, good reproducibility and stability, and the excellent anti-interference to other electroactive molecules and Cl-. Upon utilized for measuring glucose concentrations in human blood serum samples, the detection results on Co4N-NSs are accurate and satisfying as well. This work opens a new possibility for boosting electrochemical catalysis abilities of Co4N samples by the structure design.

High-performance non-enzymatic catalysts based on 3D hierarchical hollow porous Co3O4 nanododecahedras in situ decorated on carbon nanotubes for glucose detection and biofuel cell application.

In this work, high-performance non-enzymatic catalysts based on 3D hierarchical hollow porous Co3O4 nanododecahedras in situ decorated on carbon nanotubes (3D Co3O4-HPND/CNTs) were successfully prepared via direct carbonizing metal-organic framework-67 in situ grown on carbon nanotubes. The morphology, microstructure, and composite of 3D Co3O4-HPND/CNTs were characterized by scanning electron microscopy, transmission electron microscopy, micropore and chemisorption analyzer, and X-ray diffraction. The electrochemical characterizations indicated that 3D Co3O4-HPND/CNTs present considerably catalytic activity toward glucose oxidation and could be promising for constructing high-performance electrochemical non-enzymatic glucose sensors and glucose/O2 biofuel cell. When used for non-enzymatic glucose detection, the 3D Co3O4-HPND/CNTs modified glassy carbon electrode (3D Co3O4-HPND/CNTs/GCE) exhibited excellent analytical performance with high sensitivity (22.21 mA mM-1 cm-2), low detection limit of 0.35 µM (S/N = 3), fast response (less than 5 s) and good stability. On the other hand, when the 3D Co3O4-HPND/CNTs/GCE worked as an anode of a biofuel cell, a maximum power density of 210 µW cm-2 at 0.15 V could be obtained, and the open circuit potential was 0.68 V. The attractive 3D hierarchical porous structural features, the large surface area, and the excellent conductivity based on the continuous and effective electron transport network in 3D Co3O4-HPND/CNTs endow 3D Co3O4-HPND/CNTs with the enhanced electrochemical performance and promising applications in electrochemical sensing, biofuel cell, and other energy storage and conversion devices such as supercapacitor. Graphical abstract High-performance non-enzymatic catalysts for enzymeless glucose sensing and biofuel cell based on 3D hierarchical hollow porous Co3O4 nanododecahedras anchored on carbon nanotubes were successfully prepared via direct carbonizing metal-organic framework-67 in situ grown on carbon nanotubes.

Fabrication of Stretchable Copper Coated Carbon Nanotube Conductor for Non-Enzymatic Glucose Detection Electrode with Low Detection Limit and Selectivity.

The increasing demand for wearable glucose sensing has stimulated growing interest in stretchable electrodes. The development of the electrode materials having large stretchability, low detection limit, and good selectivity is the key component for constructing high performance wearable glucose sensors. In this work, we presented fabrication of stretchable conductor based on the copper coated carbon nanotube sheath-core fiber, and its application as non-enzymatic electrode for glucose detection with high stretchability, low detection limit, and selectivity. The sheath-core fiber was fabricated by coating copper coated carbon nanotube on a pre-stretched rubber fiber core followed by release of pre-stretch, which had a hierarchically buckled structure. It showed a small resistance change as low as 27% as strain increasing from 0% to 500% strain, and a low resistance of 0.4 Ω·cm-1 at strain of 500%. This electrode showed linear glucose concentration detection in the range between 0.05 mM and 5 mM and good selectivity against sucrose, lactic acid, uric acid, acrylic acid in phosphate buffer saline solution, and showed stable signal in high salt concentration. The limit of detection (LOD) was 0.05 mM, for the range of 0.05⁻5 mM, the sensitivity is 46 mA·M-1. This electrode can withstand large strain of up to 60% with negligible influence on its performance.

One-pot preparation of conductive composite containing boronic acid derivative for non-enzymatic glucose detection.

The composite consisting of poly(azure A), gold nanoparticles and 4-mercaptophenylboronic acid (PAA-AuNPs-MPBA) was prepared on the glassy carbon electrode surface by using a one-pot electropolymerization protocol. The generation of poly(azure A) film, the reduction of HAuCl4 and the binding of MPBA on metallic gold were simultaneously achieved in the cyclic voltammetric scan process, which was verified by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements. MPBA on the composite could capture glucose based on the specific boronic acid-diol binding and form a stable 5-membered cyclic boronate ester, which prevented the penetration and the charge transfer of the ferri-/ferrocyanide couple on the electrode surface. The peak-current change was found to be proportional to the logarithm of the glucose concentration in the range 10nM-10µM with a detection limit of 4nM. The proposed sensor exhibited good immunity from interference of several physiological compounds, reliable reproducibility and satisfying stability and it was successfully used in the determination of glucose in human serum sample.